Process of manufacturing hard board



v0 pressing.

wing. Application to new and improved the manufacture of hard This invention relates method of procedure for board and the product.

Hard board is a hard, dense, homogeneous product made from cellulosic fibers, generally by process whereby the fibers, while wet, are heated and highly compressed and retained compressed,

until dried.

This invention is particularly directed to further procedure and steps whereby a much superior hard board product is produced.

The objects are to provide a new and improved process for making hard board products of superior strength and having other superior characteristics, to reduce cost of production of such improved products by the utilization of the process hereof, and to provide for increased production, over normal production, without increase of costly equipment which would otherwise be necessary.

In order that theimprovements hereof may be understood, it is necessary to refer to past practice such as is disclosed in, among others. the Hotchkiss Patent No. 318,841 and Shaw Patent No. 1,500,208. Briefly, a cellulose containing fiber pulp is formed on a screen or the like, to the approximate form of the finished product, which formed fiber mass has its moisture content reduced to around 50%, 25% to 75% probably practical limits, by weight by appropriate cold The moist fiber mass is then pressed at high temperature and high pressure for sufiicient time to dry such fiber mass to substantially bone dryness and there results a hard, dense and homogeneous fiber product.

The invention hereof follows the general procedure as above briefly outlined but with the additional steps in the procedure, as will be fully described herein, there is produced a product which is much improved over the elemental product. The improved product is stronger, is highly water resistant and is in every way an improved product.

In making hard board, apparently any fibrous cellulosic material, such as sugar cane'bagasse, straws, various kinds of wood pulp, waste paper, sawdust and the like, may be used as the raw material. The raw material, for example, sugar cane bagasse, is digested for a suitable time at a suitable temperature to put it in condition for mechanical refining. The bagasse may be digested with water only for about 2 to 3 hours at about to pounds pressure, or digested with about 8% of lime for about 2 hours at about 40 lbs. pressure. Raw cotton as the basic material needs no digestion but may be refined directly if May 5, 1934, 726,218

caustic is added to assist and accelerate initiation of hydration of the fiber. Other fiber materials may be given a preparatory treatment in i accordance with the treatments as above pointed out but modified as maybe necessary according to the properties of the raw material used, aswill be readily understood by those familiar with the handling of fiber materials.

The object of the preliminary treatment is to break down or soften or disintegrate the binding and incrusting materials of the fibers sufiiciently that the fibers may be said to be in the initial or incipient stage of hydration. It is to be understood that the preliminary or first step of treatment does not necessarily involve hydration; it is a step to put the fiber in condition for hydration.

In the next step of the process, the initially prepared fiber is mechanically refined, that is, it is beaten or refined in a beater, Jordan, Clafliin, Bauer or like or equivalent refining machine. The refining step is carried sumciently far to obtain a good fiber separation and initiate hydration. This hydration referred to here is not necessarily hydration as usually considered by the paper-maker, but is really only the initiation of the hydration referred to by the paper maker, although further hydration is in general beneficial, though unnecessary. Hydration as employed herein refers to softening of the fiber, that is, to the condition whereby, upon pressing, the fibers can be solidly compacted and consolidated.

As is usual in papermaking, the fiber hereof is handled, in its various stages of processing, in

'water suspension in which the fiber is present in the amount by weight of 5% to approximate, with the usual content about 2% to 1%.

The fiber material, during the digestion step, becomes saturated with water, which fact makes possible the utilization of one of the steps in-this process.

Due to the fact that thefiber is saturated and in water suspension, it becomes possible to apply to the fiber very advantageously a combination binding and waterproofing substance. In the preferred form of the invention it has been found that tung oil, if added to the fiber suspension, particularly in the relatively small amount of about 1% to 5%, will almost quantitatively be adsorbed by the fiber, probably principally as an exterior coating or film thereon. The cellulose containing fiber has a high degree of surface attraction for the oil and readily picks it up from the water of suspension, and due to the fact that the fiber is water saturated and that the oil is 2 not soluble in the water, the film of adsorbed oil is largely localized on the fiber surface.

Whereas the specific example above given specifically refers to tung oil, it is to be understood that equivalent substances classed generally as drying oils, for example, cashew nut oil may be substituted, also linseed oil or various synthetic resins in an intermediate stage of polymerization and various other liquid form water insoluble binders may be used.

The oil is preferably added at the refiners where the agitation of the fiber suspension is severe, whereby the oil is rapidly brought into contact with the fiber. The oil, though, may be added at any convenient point where there is agitation which will bring the oil and fiber into contact.

The fiber, carrying an adsorbed film of tung or equivalent oil, is formed or sheeted on a screen according to the general practices of papermaking and by suitable drainage and/or pressing operations the water content is reduced to about 50% (by weight) with allowable variation of be.- tween about 25% to 75%.

The fiber mass formed as above is now placed in a heated press capable of exerting considerable pressure and is therein compressed and dried.

The press should have at least one face formed of a screen supported on a press face or both faces may be so arranged. The screen serves as escape channels for water and steam to leave the board while it is being pressed. If one face of the product is to be smooth, then, of course, only one screen is used and the other press face is formed of a smooth plate.

In making a finished pressed product about thick, the formed wet fiber mass heretofore described and about in thickness is placed in the press, the faces of which are heated to a temperature of 325 F. (with operating variation of about 50 to 75 F. plus or minus) and the press is rapidly closed to exert a pressure of 200 to 225 pounds per square inch on the fiber mass. Press pressure may be varied through a wide range, depending the finished product. With average fiber and a wet mass of about V2 in thickness and temperature of 325 a pressure of about 200 to 225 pounds per square inch will produce a product having a density of about 1. The press pressure should follow up any shrinkage to the fiber mass as it dries and the pressure should be maintained substantially constant.

The product as described will be dried, under the conditions outlined, in about 15 minutes. According to this invention, there are several things which happen during the drying of the fiber mass subject to the simultaneous high pressure and temperature. On the one hand, the fiber of the mass is subjected to a high pressure cooking which apparently first acts to carry further the incipient hydration referred to and then as the fiber dries, while held in intimate contact due to the press pressure, tocause the contacting hydrated fiber surfaces to adhere one to another. On the other hand, the adsorbed surface films of tung oil are somewhat polymerized and/or oxidized.

Tung oil is primarily considered as a polymerizing oil, as a material which, when subjected to heating, becomes more dense molecularly, to become a hard and dense irreversible final product.

There is some reason to believe that oxidation to some extent, at least, enters into the change in tung oil, so therefore this was also above mentioned as a possibility and in the useof the words on density and hardness desired for.

polymerizing or polymerized herein there is comprehended hardening due to oxidization or other process brought about through the application of heat.

Under the conditions as above outlined, whereas, at about 325 F., pressure of 225 pounds and time 15 minutes, the product will be pressed into final form and dried, the polymerization of the tung oil will have only been initiated but not completed. In order that polymerization of the binder (tung oil) may be completed without tying up the expensive press equipment, the product is removed from the press as soon as it becomes dry, at which time the binding action, due to the hydration bond and preliminary polymerization, has been sufiiciently developed to hold the,

product together and to all visual inspection, to have produced a finished product.

While the product as above will have produced a usable material, there still remains therein the undeveloped additional strength and water-proofing which will be afiorded on completion of polymerization of the binder. To complete the polymerization, the product from the press is promptly, with as little heat loss as possible, piled in mass and protected from heat loss by any kind of heat insulating covering. A convenient sized mass of boards may be a pile of about 100 sheets of 4' x 12' board. or course, it is not to be supposed that heat loss from the massis to be entirely prevented, but sufficient heat insulation material should be used in the protective covering to retain a considerable amount of heat in the protected mass for a considerable time, and as an example, it is suggested that the heat insulation material should have sufiicient insulation effect to prevent the temperature of the mass falling below 200 F. within 2 hours after removal from the press. In case the mass of material as above described is not of sufficient volume or if impractical to sufficiently insulate to prevent too rapid heat loss, such conditions may be compensated for by the addition of heat from any convenient source.

When the press product is massed and held in heated condition for an appreciable time, say for from 6 to 24 hours, as above described, the binder and waterproofing material, the tung oil, proceeds with its polymerization and the strength and waterproofing obtained by the use of such binder is developed and becomes effective to greatly increase the strength of the final product and provide very considerable water resistance.

As an example, the strength of a fiat board form product made in accordance with the above procedure and containing 2% of tung oil, as compared to a similar product without added tung oil, increased from a tensile strength of about 4,000 pounds per square inch to a tensile strength of 6,000 pounds per square inch or more, and the water resistance increased from an absorption of about 100% in two hours to about 15% in 24 hours.

The striking improvement in physical qualities obtained by the application of the inventions hereof is ascribed to the fact, as was pointed out, that since the fibers are saturated when the tung oil is added, the tung oil so added is probably adsorbed principally as a surface film on the fibers and does not go into the fibers and that, therefore, even such small amount of tung oil as about 2% is completely utilized as a binder between fibers to firmly secure together contiguous fibers at all points of contact and to substantially completely waterproof the surface of each individual fiber.

The practical upper limit for the tung oil used appears to be about 6%, though the use of up to 10 or 12% shows some advantage though in decreasing increments as the amount of tung oil added is increased. The greatest advantage from the use of the invention is realized with the lower percentages of addition of tung oil, that is, for additions of about from 1 to 3%.

The invention having been fully described above:

I claim:

1. The process of producing a hard, dense and highly water resistant product from bagasse, wherein the bagasse is softened by digestion and refined mechanically to a fibrous state, such fiber then having admixed therewith and therethrough a polymerizing substance, and together with such polymerizing substance subjected to elevated temperature for a time suificient to thoroughly heat the mass thereof and initiate polymerization, such mass then, while in heated condition, protected by a heat insulating material and maintained so protected until substantial polymerization has taken place.

2. The process of manufacture of fiber products which consists in thoroughly distributing a polymerizing oil throughout a water suspension of fiber, the suspension water then largely removed to provide a felted fiber mass, which fiber mass is then submitted to the application of high pressure and is heated to initiate polymerization of said oil, the compressed and heated mass then insulated sumciently that the loss of heat therefrom is slow and said heated mass maintained so insulated until said oil has substantially completely polymerized.

3. The process of producing a hard, dense and water resistant product from vegetative fiber wherein the fiber material, softened by a digestion, is mechanically separated into fibrous state, the fiber in suspension in'water having added thereto and thoroughly admixed therein a water insoluble heat-hardening binder material, the fiber and binding material then having a large portion of the water of suspension removed therefrom to form a wet felted mass, the wet felted mass having the binder material disseminated therethrough then subjected to high pressure, at elevated temperature between pressure faces providing for the escape of steam from the wet mass, the pressure being maintained until the mass is substantially bone dry, the pressure then released and the hot compressed mass removed from the press and held subjected to conditions preventing rapid dissipation of heat therefrom.

4. The method of manufacture of articles composed of fibrous material, having interspersed throughout a heat-hardening binder, wherein such articles are first heated to initiate hardening of the binder and then a plurality thereof are subjected for a limited time to heat and are then protected from heat loss with heat insulation material to retain the sensible heat thereof for a considerable time and thereby maintain conditions for further hardening of the binder.

6. The process of producing a hard, dense,

strong and water-resistant fiber product from fibrous material, wherein the fibrous material, together with a small content of polymerizable binder is first subjected to simultaneous application of heat and pressure, to compact the product and initiate polymerization of the binder substance, is subsequently piled in mass and protected by heat insulation, whereby the heat of the mass is retained for a time suflicient to increase appreciably the polymerization of the binder substance.

7. The method of curing a heat hardening binder material wherein the binder material is heated and subsequently substantially enclosed in a heat insulation material to retain the sensible heat thereof and thereby subject the material to a prolonged period of treatment without further application of heat from an external source.

8. The process of manufacture of a fiber board wherein a small amount of a polymerizable substance is thoroughly distributed throughout a mass of fiber and the whole is subjected to high press pressure with the simultaneous application of heat, the mass compressed and heated, removed from the press, insulated against heat loss and maintained so insulated until the polymerizable substance is substantially polymerized.

9. The method of curing a product, composed of mixture of a heat hardening binder material admixed with a filler material, wherein the admixed binder and filler are subjected to pressure and heat simultaneously for a time sufficient to substantially set the binder, the set product then maintained, by the use of heat insulation material retardingv the cooling thereof in a heated condition, not under pressure, for an extended -time sufiicient to cure the binder material.

10. The process as described in claim 6 .wherein, in the final step of polymerization or curing of the binder, additional heat from an independent source is supplied to the mass to substantially compensate for the normal heat loss and thus to maintain the mass at a substantially elevated temperature.

11. The process as described in claim 8 wherein heat is applied to largely compensate suchheat loss as may occur.

FERGUS A. IRVINE. 

